1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a small single use gas turbine engine with oil-less bearings.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine is a very efficient machine for converting energy contained in a fuel into mechanical energy used to drive a generator or propel an aircraft. In an industrial gas turbine engine (IGT), weight is not an issue so the engine can be large and heavy. The most important factor in an IGT is the overall engine efficiency. Combined cycle gas turbine engines are used to improve the efficiency of the engine. In an aero engine used to propel an aircraft, weight is an important factor. Higher engine performance is exchanged for lighter weight. In both of these engines, another major factor is making these engines have a long life period. The longer an engine can last, the lower becomes the overall cost of purchasing the engine.
Recently, single use gas turbine engines have been used to power unmanned aero vehicles (UAV) such as a cruise missile or an aero drone. In a cruise missile, the engine is used only once for obvious reasons and has a very short life time of about one hour. In an aero drone such as that used for video observation, size, weight, and hover time are the most important factors. The engine is used once and for a short time period until the fuel is used up. The hover time is the time that the aircraft can be flown over the intended target. The longer the time, the lower the number of aircraft needed.
In these UAVs, the engine is small in the order to a few hundred pounds thrust or less. At this small size, the rotor shaft must rotate at very high rotational speeds in order for the performance of the engine to be efficiency enough for use in these aircrafts. In a normal gas turbine engine (non-single use engines) the rotor shaft is supported by bearings that can be cooled by passing a lubricant through the bearings. With this type of bearing lubrication system, an oil reservoir tank is required as well as an oil pump, an oil filter, a lubrication system and other parts to provide a fully functioning bearing lubrication system for the engine. This lubrication is not a major problem for use in the larger and multiple use engines. However, for a single use and small engine, a separate bearing lubrication system would add a significant amount of weight, size and complexity to the little engine. Space is limited in a small aircraft such as a cruise missile or drone. Any additional weight added to the aircraft means that less fuel can be carried, and therefore the hover time is reduced. If the bearings can be cooled and lubricated without the need of a separate bearing lubrication system, then extra fuel can be accommodated on the aircraft and the hover time can be increased. Without adequate bearing cooling, a small gas turbine engine that operates at very high rotational speeds will burn up the bearings very quickly. Therefore, a small UAV powered by a small gas turbine engine is not practical using prior art technologies.
It is therefore an object of the present invention to provide for a small gas turbine engine that is used for a single flight in which the bearings can be adequately cooled and lubricated without the use of a separate bearing lubrication system in order to reduce the weight and size of the engine.